Add nvme detection support and refactor code

What's Changed

• fix travis config for python 3.7 by using xenial by @fredericlepied in #86
• Move smart utils to its own module by @elfosardo in #85
• Use pure argparse by @elfosardo in #89
• Fix error cpu benchmark with Python 3.x by @elfosardo in #88
• Basic support for nvme devices by @elfosardo in #91

Full Changelog: 0.20.1...0.21.0